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P. 4099. A sample of water of mass m1 and of temperature t1 is in a thermos flask, and warmer water of mass m2 and of temperature t2 is poured to it. After the themal equilibrium is reached the temperature is measured. Next time, because we are curious, we swop the two samples of water, so the colder water of mass m1 and of temperature t1 is poured into the thermos in which there is the other sample of water of mass m2 and of temperature t2. Surprisingly it is found that the equilibrium temperature in the second case is different from the one measured in the first time.

a) How can you explain this difference?

b) The difference between the two equilibrium temperatures is 1.9 oC. What can you deduce from this?

Data: m1=300 g, t1=20 oC, m2=600 g, t2=80 oC.

(4 points)

Deadline expired on 11 November 2008.

Statistics on problem P. 4099.
 118 students sent a solution. 4 points: 80 students. 3 points: 15 students. 2 points: 15 students. 1 point: 4 students. 0 point: 2 students. Unfair, not evaluated: 2 solutions.

• Problems in Physics of KöMaL, October 2008

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